Optical design of a Butterfly lens for a street light based on a double-cluster LED

We construct a precise optical model of the cluster LED and propose a design of a peanut form lens to achieve an optical utilization factor of 45% and uniformity of 1/2.7. Then we propose a new design of so-called Butterfly lens with unequal tilt design aimed to serve a double-cluster LED but with a tightened size. The optical utilization factor of the Butterfly lens is about 43.8%, the uniformity is around 1/2.7, and an averaged illuminance of 14 lx, which could meet almost all types requested by IESNA. The design of the Butterfly lens is proven workable for a double-cluster LED.